Perfluoropolyethers have long been recognized for their outstanding thermal properties and their wide liquid ranges. These properties render them useful as hydraulic fluids, heat exchange fluids and lubricants. For many applications, it is desirable to have a fluid with very good low temperature properties (e.g. low pour points) as well as good high temperature stability. It is recognized in the art that one way of extending the low temperature liquid range of a fluid is the incorporation of methylene oxide units in the polymer. The low energy of activation for rotation about a carbon-oxygen bond gives the fluid added mobility at low temperatures. Unfortunately, typical vinyl polymerization techniques such as those used to make polytetrafluoroethylene oxide and polyhexafluoropropylene oxide (DuPont Krytox.TM.) cannot be used to make a difluoromethylene oxide containing polymer.
Sianesi and coworkers describe the synthesis of polymers of the general formulae CF.sub.3 --O--(CF.sub.2 --O).sub.n --CF.sub.2 --C(O)F, CF.sub.3 --(O--CF.sub.2).sub.n --CF.sub.2 --C(O)F and CF.sub.3 --(O--CF.sub.2).sub.n --O--C(O)F. See French patents 1,531,902 and 1,545,639. The polymeric mixture was obtained by reacting difluorocarbene (generated in situ by the pyrolysis of hexafluoropropene) with molecular oxygen. Although the polymers contain reactive end groups such as acyl fluoride and fluoroformate groups which limit their stability, the polymers represented a major breakthrough.
Gerhardt and Lagow describe the synthesis of perfluoropolyethylene oxide by direct fluorination. J. Chem. Soc., Perkin Trans. I, 1321 (1981). The authors also report the formation of a partially fluorinated polymer obtained in low yield when polymethylene oxide (polyformaldehyde) was slowly reacted with dilute elemental fluorine at -78.degree. C.